[opendtv] Re: Senators Support Funds to Fill DTV Gaps
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 3 May 2009 18:42:05 -0400
Dale Kelly wrote:
> It was well know technically, from the beginning, that
> sufficient channels were not available to replicate
> current analog channels, especially after losing the
> top UHF tier.
Was this true during or after the transition? I thought that after the
transition, the much less stringent tabboo rules would compensate for
the loss of 52-69? During the transition, adjacent UHF DTV channels seem
to work quite well. In analog times, weren't something like 5 channels
required between UHF stations in any given market (a legacy from the
selectivity limitations of early UHF receivers)?
> It was also well understood that replication could not
> always be achieved at the allocated power levels but the
> FCC had little choice given the available spectrum.
I guess the greens should be glad about this. The max ERP from analog
UHF stations was 5 MW, I think. So in terms of just UHF coverage, if a 5
MW UHF analog channel always went to a 1 MW digital UHF, all would be
well (7 dB less power in digital, should be close to equivalent
coverage). Unfortunately, it doesn't work that way every time, in either
band, as we have discussed already.
> However, I was there (at the FCC) during the initial
> allocation discussions and have a slightly different
> perspective. Are you aware that the FCC originally
> calculated that many digital UHF stations, replacing
> many VHFs, would require up to 5MW ERP to replicate
> current coverage?
You made me aware of this some time ago, that's how I knew.
> However, the fact that a new set of politicians
> understands that need and is willing to fund it is
> refreshing.
Indeed it is. That was my reaction to the article.
Aside from special circumstances, involving large geographic obstacles,
*extending* digital coverage of a big stick via on-channel repeaters
seems like a losing proposition to me. Making reception easier with the
OCR, within relatively close range of the big stick, where the signal
from the big stick is still strong in surrounding areas, sure.
(I think that what makes DVB-T2 interesting is that it can extend the
max distance between towers of a SFN to something like 4X what was
practical with DVB-T. So that in European countries that already use a
relatively dense mesh of translators for analog, with low power big
sticks 30-50 miles apart or so, for nationwide networks, those could
potentially be transformed into a SFN. You'd have a "dense-enough" mesh
of towers already in place, needed for wide area coverage with a SFN. I
don't think this works reliably enough with DVB-T or, even more so,
8T-VSB.)
Bert
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